The present invention relates to an enclosure services processor card arranged to selectively split a fibre-channel arbitrated-loop (FC-AL).
Referring now to FIG. 1, a backplane 10 suitable for being housed in a 19″ 3U rack/shelf is shown schematically. For clarity, detail such as tracking or peripheral devices such as memory chips have been omitted where this detail is not necessary for describing the present invention.
The backplane further includes a pair of edge connectors (not shown), each adapted to receive one of a potential pair of plug-in enclosure services processor cards 4 (only one shown), each including a respective processor 7. The processor may, for example, operate according to the SCSI Enclosure Services (SES), SCSI Accessed Fault-Tolerant Enclosure (SAF-TE), SCSI Enclosure Services (SES) or Intelligent Platform Management Interface (IPMI) enclosure management protocols.
One or more of a range of SES Processor cards 4 can be plugged in and populated to provide advanced features, such as Ethernet, Direct Attach Fibre or Simple Network Management Protocol (SNMP). As described in related patent application entitled “Data Gathering Device for a Rack Enclosure” naming Aedan Diarmid Cailean Coffey et al as inventors (published as US 2002/0054477 A1), the two processors 7 arbitrate between one another as to which will be responsible for the provision of enclosure services.
When one processor takes responsibility, by default, the other processor goes into a “dead till enabled” standby mode. If the responsible processor for some reason fails, then the other processor will take over responsibility for environmental monitoring.
A further plurality of edge connectors (not shown) are mounted on the backplane, and a set of Fibre Channel disk drives 80 are inserted into associated slots in the rack system where they connect at their rear to respective edge connectors and are thus interconnected via the backplane. Such disks include two pairs of fibre channel ports, each pair connecting to a respective one of a pair of Fibre Channel-Arbitrated Loops (FC-AL) designated Loop A and Loop B. Each disk further includes an Enclosure Services Interface (ESI) port (also more properly known as SFF-8067. SFF=Small Form Factor). This is conventionally used to provide communication between one or more of the disks and an enclosure services processor located on either a card connected to the backplane or even incorporated on the backplane.
A host application running on one or both of host machines Host A or Host B communicates with each of the disks 80 via one of the fibre channel loops. When the host application wishes to send and receive enclosure services information, for example, using the SES protocol, it sends a request to a pre-determined one of the disks. When the receiving disk processes the request, it determines that the request is an enclosure services request and forwards this request through its ESI port. Alternatively, the SES processor can report status to and receives commands from the host application out-of-band via an RS-232 connection (not shown).
In any case, for each disk 80, each of the sending and receiving ports for loop A and loop B are brought onto a respective processor card 4 where they connect to a hub 6. Conventionally, the hub comprises a plurality of port bypass circuits (PBC) each employed to connect a respective disk in a loop and to bypass ports where no disk is inserted in the slot. These circuits enable the fibre channel arbitrated loop (FC-AL) to be opened and closed and thereby dynamically reconfigured if a device is added or removed to the FC-AL. The PBC comprises a 2-input multiplexer and a switch connecting either one of the inputs to the output. The PBCs are connected in sequence such that the output of each PBC acts as one of the inputs for the next PBC. The loop is completed by connecting the output of the last device in the loop, in this case the Host A to one of the inputs of the first PBC (PBC1).
For example, looking at hub port PBC2, it can be seen that the output of the preceding hub port, namely PBC1, is transmitted both to hub port PBC2 and to the input of Disk 2. The response from Disk 2 is transmitted back through the hub port PBC2. In use, if a hub port (in this case PBC2), detects that a device is connected to it, then the PBC directly connects the response signal from the attached device to the PBC output. For clarity, the detection circuitry is not shown for all circuits, however, in each case the output signal from a device whose presence is being tested is detected.
If however, a hub port detects that a device is not connected to it, or is not responding, it directly connects the input from the preceding PBC to its own output. This acts to close the associated PBC and bypass the hub port thereby allowing the loop to remain intact. This prevents a failing device or connection from bringing down the entire loop.
If it is desired to add a new device, at port PBC1 for example, the loop opens automatically to add the new device without manual intervention, by toggling the position of the corresponding PBC switch. By this, the hub allows hot plugging; the ability to add and remove devices while the loop is active. In future versions of FC-AL, before a new device is allowed to be inserted in the loop, the hub will, at a minimum, verify valid signal quality. If a device exhibits poor signal quality or inappropriate clock speed, the associated PBC switch will remain toggled to bypass the hub-port, thereby allowing the other nodes on the loop to continue without disruption.
Arbitrated loop hubs may provide from 1 to 16 hub ports, i. e. n=16, with accommodation for more devices accomplished by cascading hubs together. A cascade is built by simply connecting a hub port, in this case PBCEX of one hub to a hub port on the other, preferably with fibre optic cabling. Alternatively, a second host, in this case Host B, can be connected to the hub port, thereby providing redundancy (hot-standby) for Host A or load-sharing access to the loop devices. In any case, the total loop circumference is extended through additional hubs until the desired port count is reached.
However, such hubs have the disadvantage that the sequence of ports in the FC-AL through which a signal is transmitted is fixed by the internal wiring of the hub. Further such systems only allow the connection of one port to another thereby acting to include devices in the FC-AL.
In co-pending application entitled “Cross-Point Switch for a Fibre Channel Arbitrated Loop” naming Aedan Diarmid Cailean Coffey as inventor the hub 6 comprises a cross-point switch which is used to connect each of the disk sending ports to a receiving port of another disk in one of Loops A or B in a configurable manner. Thus, disks (or repeaters or retimers if necessary) may be ordered in either loop in any desirable manner and furthermore, or they may be spaced apart in the loop in a manner that smoothes the signal level throughout the loop.
In order to configure the cross-point switches, the processor responsible for the shelf needs to determine which disks are present. The processor then determines the switches that are to be closed to link each of the disks 80 in whichever of Loops A and B are connected to its hub and relays this information to the cross-point switches.
It will be seen, however, that with all devices on the same loop, the overall throughput of the host applications connected to the loop is limited to the bandwidth of the loop. Thus, even if one or more host applications are accessing the devices on Loop A while other host applications are accessing the devices on Loop B, the maximum data rate is still limited by the bandwidth of the loop.